Secret signaling system



Nov. 14, 1950 c. E. ATKlNs SECRET SIGNALING SYSTEM Original Filed Aug.11, 1944 kai km @SEEE JNVENTOR. C4 RL 50W/wo Anf/Ns 1] Wma/,4M ATTORNEYSNov. 14, 1950 c. E. ATKINS SECRET SVIGNALINE SYSTEM 2 Sheets-Shet 2Original Filed Aug. 11, 1944 1%* Wmwmmww A TTORNEYS Patented Nov. 14,1950 SECRET SIGNALING ASYSTEM VCarl Edward Atkins, Elgin, Ill.,vassignor to Tung- Sol Lamp Works, Inc., Newark, N. J., a corpo'-rationof Delaware Original. application August '11, 1944, Serial No.549,015. Divided and this application February 7, 1950, Serial No.142,888' Y 2 Clails.

vThis invention relates to secret signaling and constitutes a divisionof my application for United States patent, Serial No. 549,015, ledAugust 1l, 1944, and entitled Secret Signaling System.

"More particularly, my inVention comprises a system whereby intelligencemay be scrambled at one station and transmitted from that station forreception and decoding at `a plurality of other stations withoutdangerof detection by unauthorized interceptors of the transmitted scrambledintelligence. Briefly and in general, the system of the presentinvention comprises the like treatment at each station of capriciouslyvarying energy available at each station and the subsequent utilizationof suchv treated energy for scrambling at the transmitting station thesignal to Vbe transmitted and for unscrambling, at the other stations,the received energy. The like treatment'of the varying' energy at eachstation may be effected in various ways. For example, a suitablecapriciously varying signal such as a delayed replica of signalintelligence or noise could be usedV to scramble the signalVintelligence to be transmitted and received andsuch capriciouslyvarying energy ornoisefmay also be further treated lor modified by asignaluniformly varied in either voltage or frequency. Thus in generalsecrecy is achieved in the system by like treatment known only to thestation concerned of energy which may or may not beVv known to aneavesdropper and theV scrambling of the transmitted signal with suchtreated energy.

For a better understanding of the invention reference may ber had to theaccompanying drawings, of which Fig. 1 is a diagram explanatory of theinvention; and Y Fig; 2'is a block diagram illustrating one em-Vbodiment thereof.

The term scrambling as'used` herein relates to vfthe'mixing orcompounding of an intelligible signal `vvith'other signals to form anunintelligible result for purposes of transmission to another station.

The underlying theory of the system of the invention will best beunderstood by reference to Fig, 1 which represents diagrammatically thesecret transmission of intelligence from a single transmitting station Ato each of a plurality of receiving stations B. At station A and at eachof stations B there is available capriciously varying energy which may,for example, be that radiated from a separate station C. At station Aand also at each of the stations B are like means for treating theenergy received from C. Such means may be formal scrambling devicesknown to the art or other scrambling means hereinafter described may beemployed. At station A the capriciously varying energy from source C isfirst treated by the scrambling means at that station andthen the signalto be transmitted is scrambled with the so treated capriciously varyingenergy and radiated to the receiving stations. At each station B thecapriciously varying energy from station C is received and likewise theradiated mixture, including the signal, is received from station A. Aseach station B includes a scrambling means identical to that at stationA, the capriciously varying energy can be similarly treated-'and thelsignal mixture decoded Aby using the treated capriciously varyingenergyV for unscrambling the signal'mixture. Thus although aneavesdroppermight pick up the energy radiated from C and also that fromstation A, he would not-be able to decipher the signal. This is sobecause in order to get a clue to the deciphering or decoding of amessage, an eavesdropper Vdepends upon getting an intelligible result.The energy radiatedl from source Cy contains no signalias it is merelycapriciously varying energy. The mixture radiated from station Aincludes components corresponding to the energy radiated from C,components introduced by the scrambling device'and theactual signalintelligence. If the energies from source C and station A were comparedby the eavesdropper, the result, being the signal scrambled by thescrambling device at station A, is not intelligible. However, at thevarious stations B, the signal can be detected because of the inclusionin the station equipment of scrambling means identical with' that atstation A.

In Fig. 1 the sourceC of capriciously varying energy has been indicatedas being a separate station transmitting energy to station A and to allstations B. Obviously this source could as well belocatecl at stationAor at any station B.

Fig. 2 illustrates diagrammatically a system embodying the invention. Inthis figure random noise impulses produced by a noise generator atstation A, are used, after formal preparation, to scramble theintelligence transmitted from that station. Key 'I is the source of thesignal intelligence to be transmitted and it actuates the main Scrambleror gate 6, passing energy to the main transmitter 8. The output of noisegenerator 60 is radiated directly by auxiliary transmitter 2. In orderthat the noise may be used to scramble telegraph signals using gates asinstrumentalities, it is necessary to select a certain 3 specificportion of the noise spectrum and prepare it for application toscrambler or "gate 6. Accordingly, energy from noise generator 60 is fedto a scrambler 4a, to which is also applied energy from a variablefrequency oscillator 62, the frequency of which is shifted in apredetermined manner by electro-mechanical means 63 activated by a motor64. Scrambler 4a is any suitable device known in the art forheterodyning the energy received from noise generator 60 with the energydelivered by oscillator 62. The output of Scrambler 4a is fed to a bandpass filter 65 which stations. Thus an unauthorized intercepter of thetransmitted mixtures can not, from either mixture alone or from bothtogether, determine the communicated intelligence. Various alternativearrangements within the scope of the invention will occur to thoseskilled inthe art. Preferably, the scrambling and unscrambling means ateach of the stations, particularly when the signals to be communicatedare telegraphic symbols, are electronic gates but other scrambling meanscould be employed if desired.

serves to select those frequency components that are within its band ata given time. Energy passing through filter 65 is fed to an amplitudediscriminator 66 which selects pulses having an amplitude in excess of apredetermined level, or sufficiently above the average level of thenoise energy passing through filter 65. Discriminator 66 could be, forexample, a voltage delayed diode circuit such as used as noise limitersin communication receivers. The output of discriminator 66 is fed to anelectronic switch 61 which is triggered by the impulses selected by unit66 on an on-andoff basis. That is, if one impulse turns the switch 61on, the next impulse turns it off and the next succeeding impulse turnsit on again. As electronic switches of this type are knownin the art,further description thereof is deemed unnecessary. The control impulsesfrom the electronic switch 6l are used to scramble the signalintelligence in gate 6.

At station B noise energy transmitted from transmitter 2 of station A ispicked up by antenna l2, demodulated in auxiliary receiver I3 anddelivered thereby to unscrambler Mia. In -unscrambler Illa thedemodulated noise energy is heterodyned with energy from a variablefrequency oscillator 68, the frequency of which is varied synchronouslywith that of oscillator 62 by electromechanical means 69 driven bysynchronous mot or 18, motors 64 and 'I8 being synchronously operated byany suitable means and the variations of frequency of oscillator 68taking place at a slightly later time than the corresponding variationsof oscillator 62 in order to compensate for the distance between thestations.

l The heterodyned energy delivered by unscrambler Ilia is treated as isthe output of Scrambler la at station A in order to prepare it forapplication to unscrambler unit I6, that is, it is passed through bandpass lter "I9, amplitude discriminator l0 and electronic switch 1I,corresponding respectively to units 65, 66 and 61 of station A. Un-

scrambling gate yIIS activated by the pulses It is also to be understoodthat the variable sig- V,nal energy produced by the oscillators 62 and68 and used for treating the noise need not be of a ,l constantlyvariable frequency but may follow any bling noise energy from saidsource with said predeterminedly varying energy, means at each stationconnected to said scrambling device for converting the output thereofinto energy impulses,

means at the transmitting station for scrambling signal intelligencewith the pulses delivered by said last mentioned means, atransmitter andantenna at the transmitting station for radiating they scrambled signal,means at a receiving station for receiving the scrambled signaltransmitted from the transmitting station, an unscrambling device at thereceiving station actuated by the impulses delivered by the converting`means at that station and by the received scrambled signal and meansassociated with said devices for compensatingy for. transit time of saidnoise energy and of said radiated scrambled signal whereby said lastmentioned .device yields the signal introduced at the transmittingstation.

2. The system according to claim 1 wherein said source of noise energyis located at the transmitting station and wherein means are provided atsuch station for transmitting the energy therefrom to the receivingstations for application to the scrambling device at such stations.

CARL EDWARD ATKIN S.

REFERENCES CITED The following references are of record in the.

file of this patent:

UNITED STATES PATENTS 2,476,337 Varian July 19, 1949

